Bacillus anthracis is the etiologic agent responsible for anthrax. The most deadly form of anthrax, as well as the form exploited for use as a biological weapon, is inhalation anthrax, in which spores are inhaled and germinate inside alveolar macrophages in the lung, eventually leading to a systemic infection. Although the mechanism of anthrax intoxication is relatively well understood, virulent Bacillus anthracis continues to represent a significant health threat. (See, e.g., “The Anthrax Toxin Complex” by S. H. Leppla, Sourcebook of Bacterial Protein Toxins, p. 277, J. E. Alouf (ed.), Academic Press, London (1991)).